I use plan base setting and its not possible to increase all mail boxes.
And
Lots of "Failure Notice" send for unknown address. I set "Reject" for Non exist user but it's not resolved.
When a spammer sends mail to none exist user in alias domain, mail sever creates "failure notice sender". If you set "Mail to nonexistent user" to "reject" for all domains it not affected to alias domains.
I disabled mail service for some alias domain and failure notice is stopping now.